A UN expert on executions will travel to Turkey next week to head an “independent international inquiry” into the death of Jamal Khashoggi, the Saudi Arabian journalist killed in the country’s consulate in Istanbul in October.

Agnes Callamard, the special rapporteur on extrajudicial, summary or arbitrary executions, said she would evaluate the circumstances of the crime and “the nature and the extent of states’ and individuals’ responsibilities for the killing”. She will report on the findings from her five-day visit to the UN human rights council in June.

The inquiry was being conducted at her request and three experts would accompany her, with forensic expertise among other skills, she said in an email to Reuters, declining to name them for now.

Earlier on Thursday, the Turkish foreign minister, Mevlüt Çavuşoğlu, said it was time for an international investigation and that the Turkish president, Recep Tayyip Erdoğan, had ordered preparations to be made.

The development came as western businesses moved to normalise relations with Saudi Arabia at the World Economic Forum in Davos. Riyadh has sent a large-scale ministerial delegation, which has expressed sorrow at Khashoggi’s death while at the Swiss resort.

Patrick Pouyanne, the chief executive of the French oil company Total, and Morgan Stanley boss James Gorman spoke alongside the Saudi finance and economy ministers at a panel at the Swiss ski resort.

Gorman said the murder of Khashoggi was unacceptable but added: “What is the alternative for a company like Total? To boycott Saudi Arabia? We are always against sanctions and boycotts. Who suffers from boycott and sanctions? It’s the normal people, the people on the street.”

Ueli Maurer, the president of Switzerland, said his country had moved on and wanted to build strong relations with Saudi Arabia, a rich, oil-producing kingdom that is itself a major global investor. “We have long since dealt with the Khashoggi case… We have agreed to continue the financial dialogue and normalise relations again,” Maurer said.

Saudi ministers expressed pleasure at the return of business interest in the kingdom. Finance minister Mohammed al-Jadaan said it was “absolutely sad, what happened to Jamal Khashoggi”, but added the fact that a $7.5bn Saudi bond was heavily oversubscribed earlier this month showed investors were regaining confidence.

The CIA has concluded that Khashoggi’s murder was probably ordered by the powerful Saudi crown prince, Mohammed bin Salman, and his death has left the US scrambling to provide cover for the kingdom, which has been a bedrock of its foreign policy under Donald Trump.

The Saudi effort to normalise relations with the west is facing pushback in Turkey, the UN and in British political circles.

Çavuşoğlu claimed on Monday that some western countries were trying to cover up the Khashoggi murder, and insisted the route to justice might lie through a UN-led international probe.

Saudi Arabia has refused to cooperate with Turkey, and is conducting its own judicial proceedings against 12 suspects. The case is not held in public so the evidence and defence being mounted by the accused is not known.

In the UK, one of Saudi regime’s strongest sympathisers in parliament urged the Saudis to signal their commitment to reform by allowing a British panel of MPs to go to investigate allegations that women’s rights activists are being tortured and sexually harassed in detention.

Crispin Blunt – who lost the chairmanship of the Commons foreign affairs select committee partly due to his support for UK arms sales to Saudi Arabia – has so far been stonewalled by Saudi Arabia in his efforts to access the eight detained activists. The women were arrested between May and July and then branded traitors in the Saudi press.

Blunt, a Conservative MP, has written both to the Saudi ambassador in London and to the new foreign minister, Ibrahim al-Assaf, for permission to travel to Saudi Arabia, but has not yet been given any reply.

Speaking a briefing in London, he said the panel will publish its own findings on the allegations of torture if the Saudis do not cooperate by the end of the month.

Human Rights Watch claims there have been credible reports from members of the women’s family that they have also been denied medical access, as well as maltreated.

Blunt said: “These women are celebrities of the international women’s movement so there is an enormous global focus on what is happening to them. There is a clear opportunity for Saudi Arabia to send a signal that things have changed and they could amplify that by engaging with our panel.”